we've had an incident where the customer's log file grew to 16GB (what we've set its max to), on a data size of ~4GB, despite the presence of regular backups, both full and log.

This was discovered when users were no longer able to log on because the transaction log was 'full'

In SQL Management Studio, on running the standard report "Top Transactions by Age", there is/was a transaction lurking there that belongs to the JIWA plugin scheduler, that has been there for several weeks. We restarted the service, and things returned to normal; the log was 'shrinkable' to (nearly) zero.

36 hours later, I can see that the transaction started when we restarted the service is there: